Difference will more than likely be marginal in terms of wear between the two speed ratings, but as a general rule of thumb, the higher speed rating will provide better wear at the cost of reduced ice/snow traction. Still, these differences should be minimal and not the driving factor in most cases.
I would stick with OEM size in your case, as the Nokian WR's are intended for year-round use. Minus sizing will be undesirable for summer, and plus sizing will be undesirable for winter. Just check that the speed rating is at least what was provided OEM. I believe they came with S rated, so you're fine either way.